1. Field of the Invention
The present invention relates to a method of manufacturing an electromechanical transducer such as a capacitive transducer that is used as an ultrasound transducing device, and the like.
2. Description of the Related Art
Conventionally, a micromachined member manufactured by a micromachining technique is capable of being processed in micrometer orders, and various micro functional devices are realized by using the same. A capacitive transducer (Capacitive Micromachined Ultrasonic Transducer: CMUT) using such a technique is being studied as a replacement of piezo-electric devices. According to this CMUT, ultrasonic waves can be sent and received by using vibration of a vibration film, whereby a wide-band property, especially superior in liquid, can easily be obtained.
In regards to the above technique, there is a method of manufacturing a capacitive transducer by using a monocrystal silicon vibration film disposed on a silicon substrate by bonding and the like (see U.S. Pat. No. 6,958,255, and Sensors and Actuators A 138 (2007) 221-229). In U.S. Pat. No. 6,958,255, a thermally-oxidized film is formed on the silicon substrate, and bonding of silicon substrates is performed after having removed a part of the thermally-oxidized film, whereby a portion where the thermally-oxidized film had been removed becomes a vacant gap. After the bonding, the capacitive transducer is manufactured by exposing the monocrystal silicon vibration film to form a cell that uses the monocrystal silicon vibration film as a vibration film. In Sensors and Actuators A 138 (2007) 221-229, a thermally-oxidized film is formed on a silicon substrate, and a thermally-oxidized film is formed for the second time after having removed a part of the first thermally-oxidized film. Further, a protrusion of the thermally-oxidized film that had been generated at a portion that is to be a bonding interface is removed after having formed the thermally-oxidized film for the second time, and then bonding of silicon substrates is performed. After the bonding, a capacitive transducer is manufactured by processing the silicon substrate, exposing a monocrystal silicon vibration film, and forming a cell that uses the above as a vibration film.